Graduated from and long-time star of Kärpät Oulu of the SM-Liiga, Ruotsalainen was a small player, primarily known for his exceptional speed, which often made former New York Rangers coach Herb Brooks claim without hesitation that he was the best NHL skater of his time. The Finn was the Rangers' 6th round pick (119th overall) of the 1980 NHL Entry Draft. He took his chance and signed with the Rangers, making his NHL debuts in 1981. He was a Ranger until 1986; he split the 1986-87 season between Nationalliga A's SC Bern and NHL's Edmonton Oilers. After spending the next two seasons respectively with the Elitserien's HV 71 and SC Bern, Ruotsalainen came back to North America for one last NHL season, 1989-90 NHL season, playing for the Oilers and Devils, before leaving for good to Europe - he was three times Swiss Champion with Bern, in 1989, 1991 and 1992.